The present invention relates to a process for preparing polymers or ethylene/.alpha.-olefin copolymers. More particularly, the present invention is concerned with a process of preparing ethylene polymers or ethylene/.alpha.-olefin copolymers improved in bulk density, narrow in particle size distribution and superior in polymerization operability by using a catalyst comprising a specific solid catalyst component and an organometallic compound.
Heretofore, as polyethylene preparing processes there have been known various processes using catalysts comprising various inorganic magnesium compounds such as magnesium halide, magnesium oxide and magnesium hydroxide as carriers and transition metal compounds such as titanium and vanadium supported on the carriers. However, in the case where these known catalysts are used in the preparation of so-called ultra-high molecular weight polyethylenes, the resulting ultra-high molecular weight polyethylenes are generally low in bulk density, wide in particle size distribution and inferior in the polymerization operability due to fouling and the formation of coarse particles during the polymerization.
Further, in the production of ultra-high molecular weight polyethylene fibers by a gel spinning process for which there has been an increasing demand recently, or in uniform molding, it is now absolutely necessary to use an ultra-high molecular weight polyethylene high in bulk density, narrow in particle size distribution and superior in fluidity.
It is the object of the present invention to overcome the above-mentioned problems of the prior art.
Having made extensive studies, the present inventors found out surprisingly that the conventional drawbacks could be overcome by preparing a polyethylene using a catalyst comprising a specific solid catalyst component and an organometallic compound as will be described below.